<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
         .parent{
            display: flex;
            width: 400px;
            height: 400px;
            background: red;
            /* justify-content:
            space-around:每个子元素两侧的间隔相等。所以，子元素之间的间隔比子元素与父元素的间隔大一倍。
            space-between:两端对齐父元素，子元素之间的间隔都相等。
            space-evenly:子元素与父元素之间间隔相等
             */
            justify-content: space-between;
         }
         .parent>div{
             width: 100px;
             height: 40px;
             border: 1px solid #333;
         }
    </style>
</head>
<body>
    <div class="parent">
            <div></div>
            <div></div>
            <div></div>
        </div>
</body>
</html>
